US 20070156193 A1
A method and system for improving or optimizing the collection of data from and the delivery of therapy to a patient by an implantable medical device (IMD) is disclosed which uses information about the patient's respiratory cycle.
1. A computer-readable medium programmed with instructions for performing a method of optimizing therapy delivery from an implantable medical device (IMD), the medium comprising instructions for causing a programmable processor to:
monitor respiratory cycles of a patient, including determining when an inspiration phase is occurring and when an expiration phase is occurring;
set therapy parameters to a first set of therapy parameters during the inspiration phase; and
set therapy parameters to a second set of therapy parameters different from the first set during the expiration phase.
2. A medium according to
3. A medium according to
4. A medium according to
5. A medium according to
6. A medium according to
7. A medium according to
8. A medium according to
9. A computer-readable medium programmed with instructions for performing a method of collecting hemodynamic data in an implantable medical device, the medium comprising instructions for causing a programmable processor to:
monitor respiratory cycles of a patient, including determining when an inspiration phase is occurring and when an expiration phase is occurring;
identify at least one timing reference point of a respiratory cycle; and
collect a set of hemodynamic data from the patient at intervals based on the at least one timing reference point of a respiratory cycle such that all data in the set were obtained during approximately the same portion of the respiratory cycle.
10. A medium according to
11. A medium according to
12. A medium according to
13. A medium according to
14. A medium according to
15. A medium according to
16. A medical device system comprising:
means for monitoring respiratory cycles of a patient; and
means for delivering therapy parameters that vary as a function of the phase of the patient's respiratory cycle.
17. A system according to
means for determining when an inspiration phase is occurring and when an expiration phase is occurring;
means for delivering a first set of therapy parameters during the inspiration phase; and
means for delivering a second set of therapy parameters different from the first set during expiration phase.
18. A system according to
19. A system according to
20. A system according to
The present invention relates generally to medical devices, and more particularly to implantable medical devices (IMDs).
Cardiac function varies during respiration, a phenomenon referred to as the “respiration effect.” Pressures in the right atrium and thoracic vena cava depend on intrapleural pressure (Ppl). During inspiration, the chest wall expands and the diaphragm lowers. This causes a fall in Ppl that leads to expansion of the lungs and cardiac chambers (e.g., right atrium and right ventricle), and a reduction in right atrial and ventricular pressures. As right atrial pressure falls during inspiration, the pressure gradient for venous return to the right ventricle increases. During expiration, the opposite occurs. Thus, the net effect of respiration is that increasing the rate and depth of ventilation facilitates venous return and ventricular stroke volume.
The respiration effect is typically seen earlier in the right ventricle than in the left ventricle, since inspiration and expiration tend to affect the hemodynamics of the right ventricle more directly than that of the left ventricle. The effect of respiration on the right side of the heart is subsequently observed on the left side of the heart, typically after a delay of about one cardiac cycle or more, as changes in the mechanical function of the right side of the heart are observed on the left side of the heart in the next few cardiac cycles. This time lag may become more pronounced in certain patients as cardiopulmonary functions deteriorate (for example without limitation, due to the progression of heart failure, pulmonary edema, and pulmonary hypertension).
To date, various methods have been proposed for detecting respiration with an implantable medical device (IMD). For example, minute ventilation sensors have been used to measure respiration by monitoring cyclic changes in transthoracic impedance that occur during respiration. Intracardiac electrogram (EGM) amplitude modulation has also been used to monitor respiration. A technique for monitoring respiration that uses blood pressure signals has also been proposed.
The respiration effect may cause fluctuations in a number of hemodynamic parameters that may be the subject of monitoring and/or the basis for therapy decisions. Such fluctuations may affect the ability of a physician (or an IMD) to interpret the monitored hemodynamic parameters and/or to provide (or deliver) appropriate therapy.
In certain embodiments of the invention, a method of collecting hemodynamic data from a patient includes monitoring the respiratory cycles of a patient, and identifying a timing reference point in the respiratory cycle from which to base the timing of the collection of hemodynamic data.
In certain other embodiments of the invention, a method of optimizing therapy delivery includes monitoring the respiratory cycles of a patient, and varying therapy parameters according to the phase of the respiratory cycle.
In another embodiment of the invention, a medical device system for improving data collection and/or therapy delivery is disclosed which monitors the respiratory cycles of a patient to optimize the timing of data collection and/or therapy delivery.
FIGS. 9(a) and 9(b) are timing plots illustrating alternate methods of varying therapy delivery to a patient based on respiratory cycle information.
The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings depict selected embodiments and are not intended to limit the scope of the invention. It will be understood that embodiments shown in the drawings and described below are merely for illustrative purposes, and are not intended to limit the scope of the invention as defined in the claims.
The heart and lungs are functionally linked for oxygen and carbon dioxide transport. In addition, the heart and lungs are mechanically linked through their close proximity within the equi-pressure intrathoracic cavity, neurally linked through reflex pathways, and humorally linked through endocrine and metabolic function. These functional, mechanical, neural and humoral linkages simultaneously operate to create a complex system. In monitoring cardiac function and delivering therapy using implantable medical devices (IMDs), these linkages are often not taken into account.
The “respiration effect” is an example of the result of such linkages. The effects of respiration on hemodynamic parameters tend to be exhibited in the right ventricle before the left ventricle. For example, there is typically a difference of one or more cardiac cycles in the occurrence of a given respiration effect between the right and left ventricles. This difference may become more pronounced as cardiac function deteriorates, for example, in a heart failure patient. Methods and systems in accordance with certain embodiments of the invention may therefore include monitoring of the respiratory cycle (inspiration and expiration) to improve data collection and/or to optimize therapy delivery. Certain embodiments of the invention may include, or may be adapted for use in, diagnostic monitoring equipment, external medical device systems, and implantable medical devices (IMDs), including implantable hemodynamic monitors (IHMs), implantable cardioverter-defibrillators (ICDs), cardiac pacemakers, cardiac resynchronization therapy (CRT) pacing devices, drug delivery devices, or combinations of such devices.
It should be noted that the IMD 14 may also be an implantable cardioverter defibrillator (ICD), a cardiac resynchronization therapy (CRT) device, an implantable hemodynamic monitor (IHM), or any other such device or combination of devices, according to various embodiments of the invention.
Typically, in pacing systems of the type illustrated in
In addition, some or all of the leads shown in
The leads and circuitry described above can be employed to record EGM signals, blood pressure signals, and impedance values over certain time intervals. The recorded data may be periodically telemetered out to a programmer operated by a physician or other healthcare worker in an uplink telemetry transmission during a telemetry session, for example.
The therapy delivery system 106 can be configured to include circuitry for delivering cardioversion/defibrillation shocks and/or cardiac pacing pulses delivered to the heart or cardiomyostimulation to a skeletal muscle wrapped about the heart. Alternately, the therapy delivery system 106 can be configured as a drug pump for delivering drugs into the heart to alleviate heart failure or to operate an implantable heart assist device or pump implanted in patients awaiting a heart transplant operation.
The input signal processing circuit 108 includes at least one physiologic sensor signal processing channel for sensing and processing a sensor derived signal from a physiologic sensor located in relation to a heart chamber or elsewhere in the body. Examples illustrated in
The pair of pace/sense electrodes 140, 142 are located in operative relation to the heart 10 and coupled through lead conductors 144 and 146, respectively, to the inputs of a sense amplifier 148 located within the input signal processing circuit 108. The sense amplifier 148 is selectively enabled by the presence of a sense enable signal that is provided by control and timing system 102. The sense amplifier 148 is enabled during prescribed times when pacing is either enabled or not enabled in a manner known in the pacing art. The blanking signal is provided by control and timing system 102 upon delivery of a pacing pulse or pulse train to disconnect the sense amplifier inputs from the lead conductors 144 and 146 for a short blanking period in a manner well known in the art. The sense amplifier provides a sense event signal signifying the contraction of the heart chamber commencing a heart cycle based upon characteristics of the EGM. The control and timing system responds to non-refractory sense events by restarting an escape interval (EI) timer timing out the EI for the heart chamber, in a manner well known in the pacing art.
The pressure sensor 160 is coupled to a pressure sensor power supply and signal processor 162 within the input signal processing circuit 108 through a set of lead conductors 164. Lead conductors 164 convey power to the pressure sensor 160, and convey sampled blood pressure signals from the pressure sensor 160 to the pressure sensor power supply and signal processor 162. The pressure sensor power supply and signal processor 162 samples the blood pressure impinging upon a transducer surface of the sensor 160 located within the heart chamber when enabled by a pressure sense enable signal from the control and timing system 102. Absolute pressure (P), developed pressure (DP) and pressure rate of change (dP/dt) sample values can be developed by the pressure sensor power supply and signal processor 162 or by the control and timing system 102 for storage and processing.
A variety of hemodynamic parameters may be recorded, for example, including right ventricular (RV) systolic and diastolic pressures (RVSP and RVDP), estimated pulmonary artery diastolic pressure (ePAD), pressure changes with respect to time (dP/dt), heart rate, activity, and temperature. Some parameters may be derived from others, rather than being directly measured. For example, the ePAD parameter may be derived from RV pressures at the moment of pulmonary valve opening, and heart rate may be derived from information in an intracardiac electrogram (EGM) recording.
The set of impedance electrodes 170, 172, 174 and 176 is coupled by a set of conductors 178 and is formed as a lead that is coupled to the impedance power supply and signal processor 180. Impedance-based measurements of cardiac parameters such as stroke volume are known in the art, such as an impedance lead having plural pairs of spaced surface electrodes located within the heart 10. The spaced apart electrodes can also be disposed along impedance leads lodged in cardiac vessels, e.g., the coronary sinus and great vein or attached to the epicardium around the heart chamber. The impedance lead may be combined with the pace/sense and/or pressure sensor bearing lead.
The data stored by IMD 14 may include continuous monitoring of various parameters, for example recording intracardiac EGM data at sampling rates as fast as 256 Hz or faster. In certain embodiments of the invention, an IHM may alternately store summary forms of data that may allow storage of data representing longer periods of time. In one embodiment, hemodynamic pressure parameters may be summarized by storing a number of representative values that describe the hemodynamic parameter over a given storage interval. The mean, median, an upper percentile, and a lower percentile are examples of representative values that my be stored by an IHM to summarize data over an interval of time (e.g., the storage interval). In one embodiment of the invention, a storage interval may contain six minutes of data in a data buffer, which may be summarized by storing a median value, a 94th percentile value (i.e., the upper percentile), and a 6th percentile value (i.e., the lower percentile) for each hemodynamic pressure parameter being monitored. In this manner, the memory of the IHM may be able to provide weekly or monthly (or longer) views of the data stored. The data buffer, for example, may acquire data sampled at a 256 Hz sampling rate over a 6 minute storage interval, and the data buffer may be cleared out after the median, upper percentile, and lower percentile values during that 6 minute period are stored. It should be noted that certain parameters measured by the IHM may be summarized by storing fewer values, for example storing only a mean or median value of such parameters as heart rate, activity level, and temperature, according to certain embodiments of the invention.
Hemodynamic parameters that may be used in accordance with various embodiments of the invention include parameters that are directly measured, such as RVDP and RVSP, as well as parameters that may be derived from other pressure parameters, such as estimated pulmonary artery diastolic pressure (ePAD), rate of pressure change (dP/dt), etc.
In certain embodiments of the invention, the phase difference between the derived respiratory waveforms 212, 202 may be quantified, as shown in
Another aspect of the invention enables respiration-gated data sampling.
Fluctuations in measured data due to the respiratory effect may be minimized by sampling data at a recurring point in the respiration cycle. The number of samples needed to obtain a stable average, for example, may be reduced using this method. Data collection for edema monitoring, for example, may comprise measuring the impedance value during the second or third cardiac cycle after a respiration peak (e.g., the peak during inspiration), thereby causing collection of data during approximately the same part of the respiratory cycle for each value sampled. This technique can be expanded to many other data collection schemes employed by a variety of medical device systems and monitoring devices.
Respiratory cycle 300 is shown in
For example, in one data collection scheme, sample parameter 320 may be sampled a predetermined number of cardiac cycles after a timing reference point. This data collection scheme is illustrated by interval 340, which shows data parameter 320 being sampled to obtain data sample 342, corresponding to a time interval 340 defined by the occurrence of a second cardiac event occurring in ECG signal 310 after the occurrence of the timing reference point, in this case peak 330. Of course, as would be apparent to one of ordinary skill in the art, a different point could be chosen for the timing reference point, and a different number of cardiac events may have been chosen to form the basis for interval 340, for example.
Other data collection schemes may be derived in a similar manner. For example, an interval 350 following a timing reference point (such as peak 330 in respiratory signal 300) may be defined as comprising a predetermined number of data sample intervals occurring during interval 350. Sample point 352 corresponds to a sample of data parameter signal 320 obtained using this data collection scheme, for example. A similar data collection scheme is indicated by interval 360 in
It should be further noted that, while the respiratory cycle includes two relatively distinct “phases,” i.e., the inspiration phase and the expiration phase, the term “phase” may also be used in certain contexts to describe a point or a portion of the respiratory waveform signals. For example, a zero crossing of the respiratory waveform between the end of the inspiration phase and the end of the expiration phase may define a timing reference point according to an embodiment of the invention. In that context, a data collection scheme that samples a parameter waveform during that same “phase” of the respiratory cycle would be understood as described above.
In certain embodiments of the invention, the sampled parameters may be stored, as shown by step 410 in
In certain embodiments of the invention, it may be desirable to change the timing reference point for data collection, possibly based on information acquired during data collection, or due to operator (e.g., physician) preference, for example. If a revision of the timing reference point is desired, step 418 allows for making such a change. It should be noted that in certain embodiments of the invention, it may be desirable to have multiple timing reference points defined within a given respiratory cycle. For example, it may be desirable to collect two or more sets of data, one occurring at points in time referenced to the end of the inspiration phase, and the other set of data points collected at points in time referenced from the end of the expiration phase, in one possible example. This may involve defining two or more reference timing points. Alternately, a reference timing offset (or offsets) may be employed to collect multiple sets of data, the offsets defined with reference to a single timing reference point, for example. Other minor modifications to the steps described in
Another aspect of the invention also enables respiration-gated therapy delivery.
Respiration patterns and phases may play a role in “synchronization” of the ventricular contraction. For example, cardiac pacing parameters such as atrio-ventricular (AV) delay and inter-ventricular (V-V) delay, may be varied to affect the synchronization of ventricular contractions. V-V delay may comprise the time interval from the occurrence of a depolarization event in one ventricular chamber to the programmed delivery of a pacing stimulus in the other ventricular chamber. The optimal V-V delay may be adjusted, for example, to be different during inspiration than during expiration to achieve the desired synchronization of ventricular contraction. This will be described in more detail below. Further, the respiration effect may be more pronounced in patients with congestive heart failure (CHF). For example, a preliminary analysis shows a statistically significant difference in “degree” of synchronization between RV and LV contractions which may be correlated with the respiration effect in patients with CHF.
A method of providing respiration-influenced therapy delivery is described in
Step 502 in
Step 506 includes varying the therapy delivered according to the respiratory cycles of a patient. As noted previously, cardiac pacing parameters such as AV delay and V-V delay may be varied according to the respiratory cycle to improve synchronization of ventricular contractions, according to certain embodiments of the invention.
FIGS. 9(a) and 9(b) illustrate how a particular therapy parameter, in this example, V-V delay, may be varied throughout a respiratory cycle of a patient in order to improve the therapy delivered to the patient.
Also shown in
Thus, embodiments of a METHOD OF OPTIMIZING DATA COLLECTION AND THERAPY DELIVERY BASED ON RESPIRATION are disclosed. One skilled in the art will appreciate that the invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the invention is limited only by the claims that follow.